Numerous studies have demonstrated that the photoperiod and gibberellin (GA) pathways act synergistically to promote flowering in response to inductive long days (LDs). As crucial repressors of the GA pathway, DELLA proteins were previously reported to regulate GA-mediated responses through physically interacting with several transcription factors. A very recent study reported that DELLA proteins physically interacted with CONSTANS (CO), indicating a direct association between the photoperiod and GA pathways. However, the biological significance of the DELLA-CO physical interactions remains largely unclear.

Prof. YU Diqiu and his team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted molecular and genetic investigations to elucidate the exact molecular mechanisms underlying the photoperiod and GA signaling to synergistically modulate flowering. 

In the study, the researchers found that GA-induced expression of FLOWERING LOCUS T (FT) under LDs was dependent on CONSTANS (CO), a critical transcription factor positively involved in photoperiod signaling. CO interacted with DELLA proteins in vitro and in vivo, indicating that CO functioned as a target of DELLA proteins. C-terminal parts, but not the DELLA motif or N-terminal parts of REPRESSOR OF GA1-3 (RGA), contributed to the interaction between RGA and CO. DELLA proteins interacted with CO and inhibited its transcriptional function to activate FT expression. DELLA repressed flowering partially through the CO/FT-mediated pathway. DELLA proteins were rhythmically regulated at both transcriptional and posttranslational levels. DELLA and CO proteins also antagonistically affected the expression of several other flowering-related genes.

The study results demonstrated DELLA proteins physically and genetically interacted with CO to modulate flowering under long-days in Arabidopsis. The researchers proposed that DELLA proteins acted as upstream components of CO to modulate flowering under LDs.

The study entitled “The DELLA-CONSTANS transcription factor cascade integrates gibberelic acid and photoperiod signaling to regulate flowering” has been published online in Plant Physiology.